for the rt and lle cache were added in r191129 (2009).
To my best knowledge they have never been used and route caching
has converted the inp_rt field from that commit to inp_route
rendering this field and these flags obsolete.

Convert the pointer into a spare pointer to not change the size of
the structure anymore (and to have a spare pointer) and mark the
two fields as unused.

Reviewed by:	markj, karels
Approved by:	re (gjb)
Differential Revision:	https://reviews.freebsd.org/D17062